As an alternative to standard whip antennas and roof mount mast antennas, prior art automotive antennas have included concealed window antennas that have silver printed antennas in the vehicle glazing. More recently, embedded wire antennas of quarter or half wavelength also have been used in laminated windshields and back windows. Traditionally, antenna windshields have included a wire that is embedded in an interlayer of polyvinyl butyral that is sandwiched between a pair of glass sheets. A galvanized, flat cable connector connected the wire antenna to the vehicle electronic module. Before lamination of the vehicle glazing, one end of the connector was soldered to an end of the antenna wire on the interlayer. The other end of the connector extended from the edge of the laminated glazing to provide a connection to the vehicle electronic module.
Many of the wire antenna designs in the prior art have located the wire in the middle of the windshield or glass window for better performance. For example, U.S. Pat. No. 3,576,576 titled “Concealed Windshield Broadband Antenna” assigned to General Motors discloses a pair of L-shaped wire conductors that are fed at the bottom center of the windshield, travel up the middle of the windshield, and split at top of the windshield to form a pair of L-shaped wires for AM and FM reception. U.S. Pat. No. 3,728,732 titled “Window Glass Antenna” assigned to Asahi Glass Company uses a similar pair of L-shaped wire conductors as an FM antenna with an added separated AM antenna wire that is located on the bottom of the windshield. The antenna elements are connected to a radio receiver through a switch that connects either the FM or AM antenna to the radio receiver. U.S. Pat. No. 3,845,489 titled “Window Antenna” assigned to Saint-Gobain Industries discloses an antenna that includes a first “T” shape antenna in the middle of the windshield and a second antenna that embraces the first antenna and follows the windshield frame. Both antennas are attached to a common terminal in the bottom center of the windshield. The dimensions of both antennas are complementary and produce in-phase output for AM and FM signals. U.S. Pat. No. 4,602,260 titled “Windshield Antenna” assigned to Hans Kolbe & Co. discloses an active windshield antenna with separated transmission paths for a low frequency low medium short wave region and an ultra-short wave region. The antenna wire starts from the antenna terminal and extends parallel to the frame. The antenna wire turns at the middle of the windshield so that the portion of the antenna wire on the middle of the window is the main antenna radiation element.
Such prior art designs have focused on AM and FM antennas in the VHF frequency band that have a long, visible wire in the middle of the windshield. It is generally preferred that the antenna wire should avoid a feed location at the bottom center of the windshield. That is because a printed wiper heating circuit that is typically located there can cause possible EMC interference for the antenna. Also, the antenna wire should be kept away from the 3rd visor area that is located at the top center of the windshield. Vehicles equipped with rain sensors and other windshield mounted electronics such as automatic high beam control, night vision cameras, adaptive speed control, etc. commonly have sensors that are mounted in close proximity to the rear view mirror in the 3rd visor area. Antennas in those areas are subject to RF interference in antenna reception.
There has been rapid growth in the demand for vehicle electronics so that more and more antennas are being integrated into the vehicle. Particularly at FM and TV frequencies, antenna systems require multiple antennas to provide diversity operation that overcomes multipath and fading effects. In most cases, separate antennas and antenna feeds are used to meet those demands. Therefore, there was a need in the prior art for an antenna, particularly an embedded wire antenna, that is capable of supporting multiple frequency bands that serve different applications. Furthermore, there was a need in the prior art for an improved wire antenna with multiband characteristics, good performance, and a less visible wire in the daylight opening of the windshield.